1. Field of the Invention
The present invention relates to a supported catalyst for the polymerization of olefins, to the process for the preparation thereof and to the use of said supported catalyst in processes for the polymerization of olefins.
2. Description of the Prior Art
Homogeneous catalytic systems for the polymerization of olefins based on coordination complexes of a transition metal such as titanium, zirconium or hafnium with ligands of the cyclopentadienyl type are known. Generally, these catalytic system comprise a soluble cocatalyst, such as the methylalumoxane (MAO).
These homogeneous catalytic systems show many advantages in comparison with traditional heterogeneous catalysts of the Ziegler-Natta type. In particular, they allow a careful control of the stereoregularity degree and type, the molecular weight distribution and comonomer distribution, besides making easier the use of higher alpha-olefins, diolefins and dienes as comonomers. Thus, new polymers or polymers endowed with remarkably improved properties can be obtained.
However, being soluble in the reaction system, these catalytic systems can not easily be utilized in polymerization processes which are not carried out in solution. Furthermore, the polymers obtained by processes using the above mentioned catalysts, are generally not endowed with satisfactory morphological characteristics.
In order to avoid these drawbacks, systems have been suggested based on supporting at least one component of the above mentioned catalysts on insoluble solid supports. In most cases these solid supports consist of inorganic oxides and, in particular, of silica or alumina.
In the prior art, cases are found wherein the opportunity of using supports of the polymeric type is foreseen.
In European patent applications EP-279 863 and EP-295 312 supported homogeneous catalysts comprising methylalumoxane and bis(cyclopentadienyl)zirconium dichloride are described. Besides silica inorganic supports, organic supports consisting of polyethylene or polystyrene have been used. In the preparation of the supported catalysts, use has been made of n-decane, which has the function of precipitating the methylalumoxane. These supported catalysts, after a prepolymerization treatment with ethylene in n-decane, have been used in the polymerization reaction of ethylene in gas-phase. To attain acceptable results, high amounts of methylalumoxane for each gram of solid support have been used.
In European patent application EP-518 092 catalysts of the type metallocene/alumoxane supported on polypropylene are described. These catalysts have been used in the polymerization reaction of propylene carried out in liquid monomer or in gas phase. Nothing is said about the bulk density of the polymers obtained.
Although these types of catalytic systems supported on polymeric materials are useable in processes carried out in suspension or in gas phase with acceptable yields, however they do not allow polymers endowed with good morphological characteristics to be obtained.
It has now been found by the Applicant that metallocene/alumoxane catalytic systems can be advantageously made heterogeneous by supporting them on functionalised porous organic supports. By this way it is possible to obtain catalysts in form of spherical particles, endowed with acceptable activities, able to produce polymers which duplicate the shape of the catalyst and therefore are endowed with controlled morphology and high bulk density.
Therefore, an object of the present invention is a supported catalyst for the polymerization of olefins comprising:
(A) a porous organic support functionalised with groups having active hydrogen atoms;
(B) at least one organo-metallic compound of aluminium containing at least one heteroatom selected from oxygen, nitrogen and sulphur; and
(C) at least one compound of a transition metal selected from those of groups IVb, Vb or VIb of the Periodic Table of the Elements, containing at least one ligand of the cyclopentadienyl type.
Another object of the present invention is a process for the preparation of a supported catalyst according to the present invention, which process comprises the step of contacting, in an inert solvent, the components (A), (B) and (C) among themselves.
Still another object of the present invention is a supported and pre-polymerized catalyst for the polymerization of olefins obtainable by subjecting a supported catalyst according to the present invention to a pre-polymerization treatment with at least one olefinic monomer.
A further object of the present invention is a process for the homo- or co-polymerization of olefins comprising the polymerization reaction of one or more olefinic monomers in the presence of a supported catalyst according to the present invention.
Still a further object of the present invention is a process for the homo- or co-polymerization of olefins comprising the polymerization reaction of one or more olefinic monomers in the presence of a supported and pre-polymerized catalyst according to the present invention.
The porosity (B.E.T.) of the organic support is generally higher than 0.2 cc/g, preferably higher than 0.5 cc/g, more preferably higher than 1 cc/g. In particular, supports suitably useable have a porosity comprised between 1 and 3 cc/g.
The surface area (B.E.T.) of the organic support is generally higher than 30 n/g, preferably higher than 50 m2/g, more preferably higher than 100 m2/g. In particular, the surface area can reach values of about 500 m2/g and over.
The organic support is preferably in form of particles having controlled morphology, in particular microspheroidal morphology with a diameter comprised between about 5 and 1000 xcexcm, preferably between 10 and 500 xcexcm, more preferably between 20 and 200 xcexcm.
Supports which can be used in the catalysts according to the present invention are those polymers, endowed with the above mentioned characteristics regarding the porosity and surface area, which show functional groups having active hydrogen atoms.
Examples of suitable functional groups are hydroxyl groups, primary and secondary amino groups, sulphonic groups, carboxylic groups, amido groups, N-monosubstituted amido groups, sulphonamido groups, N-monosubstituted sulphonamido groups, sulphydril groups, imido groups and hydrazido groups.
The amount of functional groups contained in the supports is generally higher than 0.2 milliequivalents (meq) for each gram of solid support, preferably higher than 0.5 meq for each gram of solid support, more preferably is comprised between 1 and 6 meq for each gram of solid support.
A class of supports particulary suitable for use in the catalysts of the present invention can be obtained from partially cross-linked porous styrenic polymers. These supports can be prepared by copolymerization of styrenic monomers, such as styrene, ethylvinylbenzene, vinyltoluene, methylstyrene and mixtures thereof, with comonomers able to be cross-linked, such as divinylbenzene, divinyltoluene and mixtures thereof. Preferred styrenic polymers are partially cross-linked styrene/divinylbenzene copolymers. Methods for the preparation of these copolymers are described, for example, in U.S. Pat. No. 4,224,415, the content of which is incorporated in the present description.
Porous polymers of this type can be functionalised by means of known methods. The most common methods to functionalise polystyrene resins are reported in xe2x80x9cComprehensive Pol. Sci., Pergamon Press, pages 82-85 (1989)xe2x80x9d.
A method for the preparation of alpha-hydroxyalkylated resins is described by I. Fujita et al. in xe2x80x9cSeparation Science and Technology, 26, 1395-1402, (1991)xe2x80x9d.
Functionalized porous styrenic polymers useable as supports according to the present invention are, moreover, those which can be directly obtained from the copolymerization of styrenic monomers with comonomers functionalized with groups containing active hydrogens or their precursors. Examples of these polymers are the styrenic copolymers functionalised with hydroxy groups, which are described in the European patent application EP-496 405.
The transition metal of groups IVb, Vb or VIb of the Periodic Table of the Elements is preferably selected from titanium, zirconium, hafnium and vanadium, more preferably is zirconium.
Transition metal compounds useable in the supported catalysts according to the present invention are, for example, the cyclopentadienyl compounds of formula (I):
(C5R15xe2x88x92m)R2m(C5R15xe2x88x92m)mMQpxe2x88x92mxe2x80x83xe2x80x83(I)
wherein M is Ti, Zr, Hf or V; the two C5R15xe2x88x92m groups, are cyclopentadienyl rings equally or differently substituted; substituents R1, same or different from each other, are hydrogen, alkyl, alkenyl, aryl, alkaryl or aralkyl radicals containing from 1 to 20 carbon atoms which may also contain Si or Ge atoms or Si(CH3)3 groups, or furthermore two or four substituents R1 of a same cyclopentadienyl ring may form one or two rings having from 4 to 6 carbon atoms; R2 is a bridging group which links the two cyclopentadienyl rings and is selected among CR32, C2R34, SiR32, Si2R4, GeR32, Ge2R34, R32SiCR32, NR1 or PR1, wherein the substituents R3, same or different from each other, are R1 or two or four substituents R3 may form one or two rings having from 3 to 6 carbon atoms; substituents Q, same or different form each other, are halogen, hydrogen, R1, OR1, SR1, NR12 or PR12; m can be 0 or 1; n can be 0 or 1, being 1 if m=1; p can be 2 or 3, preferably it is 3.
In the case of m=0, particulary suitable cyclopentadienyl compounds are those wherein the groups C5R15xe2x88x92m are selected among cyclopentadienyl, pentamethyl-cyclopentadienyl, indenyl and 4,5,6,7-tetrahydroindenyl groups, and substituents Q are selected among chlorine atoms and C1-C7 hydrocarbon groups, preferably methyl groups.
Non limitive examples of cyclopentadienyl compounds of formula (I), wherein m=0, are:
In the case of m=1, particulary suitable cyclopentadienyl compounds are those wherein the groups C5R5xe2x88x92m are selected among cyclopentadienyl, tetramethyl-cyclopentadienyl, indenyl, 2-methyl-indenyl, 4,7-dimethyl-indenyl, 2,4,7-trimethyl-indenyl, 4,5,6,7-tetrahydroindenyl, 2-methyl-4,5,6,7-tetrahydroindenyl, 4,7-dimethyl-4,5,6,7-tetrahydroindenyl, 2,4,7-trimethyl-4,5,6,7-tetrahydroindenyl or fluorenyl groups, R2 is a divalent group selected among (CH3)2Si, C2H4 and C(CH3)2, and substituents Q are selected among chlorine atoms and C1-C7 hydrocarbon groups, preferably methyl groups.
Non limitative examples of cyclopentadienyl compounds of formula (I), wherein m=1, are:
Another type of transition metal compounds useable in the supported catalysts according to the present invention, are the mono-cyclopentadienyl xe2x80x9cconstrained geometryxe2x80x9d compounds described, for example, in European patent applications EP-416 815, EP-420 436 and EP-520 732, the content of which is incorporated in the present description.
Organo-metallic compounds of aluminium useable in the supported catalysts according to the invention are, for example, linear, branched or cyclic alumoxane containing at least one group of the type: 
wherein the substituents R4, same of different form each other, are defined as R1 or are a group xe2x80x94Oxe2x80x94Al(R4)2, and optionally some R4 can be halogen atoms.
In particular, it is possible to use alumoxanes of formula (II): 
in case of linear compounds, wherein n is 0 or an integer comprised between 1 and 40, or alumoxanes of formula (III): 
in case of cyclic compounds, wherein n is an integer comprised between 2 and 40. Radicals R1 are defined as above.
Examples of alumoxanes suitable for use in the supported catalysts of the present invention are those in which radicals R1 are selected among methyl, ethyl and isobutyl groups, particularly methylalumoxane (MAO) and isobutylalumoxane (TIBAO).
A special class of organo-metallic compounds of aluminium useable in the supported catalysts according to the invention is that of compounds obtainable by reaction of aluminium alkyls or alkylhydrides with water in molar ratio comprised between 1:1 and 100:1 respectively. Compounds of this type are described in European patent application EP-575 875, the content of which is incorporated in the present description.
Moreover, organo-metallic compounds of aluminium useable in the supported catalysts of the invention are those of formula (IV): 
wherein R1 is defined as above.
The molar ratio between the aluminium and the transition metal in the supported catalysts of the invention is generally comprised between 10 and 500, preferably between 20 and 200, more preferably between 30 and 100.
The supported catalysts of the present invention can be prepared by contacting the components (A), (B) and (C) among themselves in different sequences.
An advantageous process for the preparation of a supported catalysts according to the present invention comprises contacting in an inert solvent
(A) a porous organic support functionalised with groups having active hydrogen atoms, and
(B) at least one organo-metallic compound of aluminium containing at least one heteroatom selected from oxygen, nitrogen and sulphur;
thereafter contacting the thus obtained product with
(C) at least one compound of a transition metal selected from those of groups IVb, Vb or VIb of the Periodic Table of the Elements, containing at least one ligand of the cyclopentadienyl type;
and finally recovering the supported catalyst by removing the solvent.
Another process for the preparation of a supported catalyst according to the present invention comprises contacting in an inert solvent
(B) at least one organo-metallic compound of aluminium containing at least one heteroatom selected from oxygen, nitrogen and sulphur, and
(C) at least one compound of a transition metal selected from those of groups IVb, Vb or VIb of the Periodic Table of the Elements, containing at least one ligand of the cyclopentadienyl type;
thereafter contacting the thus obtained product with
(A) a porous organic support functionalised with groups having active hydrogen atoms;
and finally recovering the supported catalyst by removing the solvent.
Yet another process for the preparation of a supported catalyst according to the present invention comprises contacting in an inert solvent
(A) a porous organic support functionalised with groups having active hydrogen atoms, and
(B) at least one organo-metallic compound of aluminium containing at least one heteroatom selected from oxygen, nitrogen and sulphur;
contacting in an inert solvent
(B) at least one organo-metallic compound of aluminium containing at least one heteroatom selected from oxygen, nitrogen and sulphur, and
(C) at least one compound of a transition metal selected from those of groups IVb, Vb or VIb of the Periodic Table of the Elements, containing at least one ligand of the cyclopentadienyl type;
thereafter contacting the product obtained by contacting (A) and (B) with the product obtained by contacting (B) and (C); and finally recovering the supported catalyst by removing the solvent.
The above indicated processes for the preparation of the supported catalysts of the invention are conducted at a temperature which is generally comprised between xe2x88x9280 and 100xc2x0 C.
The organic support can be advantageously pre-contacted with aluminium alkyl compounds of formula (VI):
R5qAlX3xe2x88x92qxe2x80x83xe2x80x83(VI)
wherein R5 is selected among alkyl, alkenyl, aryl, alkaryl and aralkyl radicals containing from 1 to 10 carbon atoms, X is selected among hydrogen and halogen atoms, q is an integer comprised between 1 and 3.
Non limitative examples of aluminum alkyl compounds of formula (VI) are aluminium trialkyls such as trimethylaluminium, triethylaluminium, triisopropylaluminium and triisobutylaluminium; dialkylaluminium halides such as dimethylaluminium chloride, diethylaluminium chloride, diisopropylaluminium chloride and diisobutylaluminium chloride; dialkylaluminium hydrides such as diethylaluminium hydride and diisobutylaluminium hydride; isoprenylaluminium. A preferred aluminium alkyl compound is triisobutylaluminium.
The supported catalysts of the present invention, before being used, can be subjected to a pre-polymerization treatment, by pre-contacting them with small amounts of at least an olefinic monomer.
The pre-polymerization treatment is generally carried out in an inorganic solvent. The amount of polymer produced in this step is generally comprised between 0.5 and 10 parts by weight with respect to the weight of the supported catalyst used.
The pre-polymerization can be advantageously carried out in the presence of aluminium alkyl compounds of formula (VI):
R5qAlX3xe2x88x92qxe2x80x83xe2x80x83(VI)
wherein R5, X and q are defined as above, or in the presence of organo-metallic compounds of aluminium (B) as above described, in particular alumoxanes. Aluminium alkyl compounds of formula (VI) are preferred.
The supported catalysts of the present invention are useable in the homo- or co-polymerization reactions of olefins.
Before the use, the supported catalysts of the invention and, in particular, those which are not pre-polymerized, can be advantageously pre-contacted with alkyl aluminium compounds of formula (VI):
R5qAlX3xe2x88x92qxe2x80x83xe2x80x83(VI)
wherein R5, X and q are defined as above, or with organo-metallic compounds of aluminium (B) as above described, in particular alumoxanes. Aluminium alkyl compounds of formula (VI) are preferred.
The supported catalysts according to the present invention can be suitably used for the homopolymerization of ethylene and, in particular, for the preparation of HDPE.
Moreover, the supported catalysts of the invention can be suitably used for the copolymerization of ethylene with olefin comonomers and, in particular for the preparation of LLDPE.
The obtained LLDPE copolymers have a content of ethylene units generally comprised between 80 and 99% by mole. Their density is generally comprised between 0.87 and 0.95 cc/g and they are characterized by an uniform distribution of the comonomeric units within the polymeric chain.
Olefins which can be suitably used as comonomers in the above said ethylene copolymers are alpha-olefins of formula CH2xe2x95x90CHR, wherein R is a linear or branched or cyclic radical containing from 1 to 20 carbon atoms, as well as cycloolefins.
Non-limitative examples of these olefins are propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexen, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, alkylcyclohexene, cyclopentene, cyclohexene, norbornene, 4,6-dimethyl-1-heptene.
The above ethylene copolymers can also contain small amounts of units deriving from polyenes, in particular from dienes, conjugated or not, linear or cyclic, such as, for example, 1,4-hexadiene, isoprene, 1,3-butadiene, 1,5-hexadiene, 1,6-heptadiene.
The ethylene copolymers contain units deriving from olefins of formula CH2xe2x95x90CHR, from cycloolefins and/or from polyenes in amounts generally comprised from 1% to 20% by mole.
Another use of interest for the supported catalysts of the present invention is for the preparation of elastomeric copolymers of ethylene with xcex1-olefins of formula CH2xe2x95x90CHR, wherein R is an alkyl radical containing from 1 to 10 carbon atoms, optionally containing lower proportions of units deriving from a polyene.
Saturated elastomeric copolymers obtained with the supported catalysts of the invention generally contain from 15% to 85% by mole of ethylene units, the rest being constituted of units of one or more alpha-olefins and/or of one non-conjugated diolefin able to cyclopolymerize.
Unsaturated elastomeric copolymers contain, besides units deriving from the polymerization of ethylene and alpha-olefins, also lower proportions of unsaturated units deriving from the co-polymerization of one or more polymers. The content of unsaturated units is generally comprised between 0.1% and 5% by weight and, preferably, is comprised between 0.2 and 2% by weight.
The elastomeric copolymers of ethylene obtainable with the supported catalysts of the invention are characterized by valuable properties such as low content of ashes and a uniform distribution of the comonomers in the polymeric chain.
Alpha-olefins which can be suitably used as comonomers in the above said elastomeric ethylene copolymers are, for example, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene.
As non conjugated olefins able to cyclopolymerize, 1,5-hexadiene, 1,6-heptadiene, 2-methyl-1,5-hexadiene can be used.
Polyenes which can be used as comonomers are those comprised in the following classes:
non-conjugated diolefins capable of cyclopolymerization such as, for example, 1,5-hexadiene, 1,6-heptadiene, 2-methyl-1,5-hexadiene;
dienes capable of giving unsaturated monomeric units, in particular conjugated dienes such as, for example, butadiene and isoprene; linear non-conjugated dienes such as, for example, trans 1,4-hexadiene, cis 1,4-hexadiene, 6-methyl-1,5-heptadiene, 3,7-dimethyl-1,6-octadiene, 11-methyl-1,10-dodecadiene; monocyclic diolefins such as, for example, cis-1,5-cyclooctadiene and 5-methyl-1,5-cyclooctadiene; dicyclic diolefins such as for example 4,5,8,9-tetrahydroindene and 6 and/or 7-methyl-4,5,8,9-tetrahydroindene; alkenyl or alkyliden norbonenes such as for example 5-ethyliden-2-norbornene, 5-isopropyliden-2-norbornene, exo-5-isopropenyl-2-norbornene; polycyclic diolefins such as for example, dicyclopentadiene, tricyclo-[6.2.1.02,7]-4,9-undecadiene and the 4-methyl-derivative thereof.
Still another use of interest of the supported catalysts of the invention is for the homo- or co-polymerization of propylene and alpha-olefins such as, for example, 1-butene. Depending on the catalytic system used, polymers showing isotactic, syndiotactic or atactic structure can be obtained.
A further use of interest of the supported catalysts of the invention is for the preparation of polymers of cycloolefins. Monocyclic or polycyclic olefinic monomers can be either homopolymerized or copolymerized also with non cyclic olefinic monomers. Not limitative examples of cyclo-olefinic polymers which can be prepared with the supported catalysts of the invention are described in European patent applications EP-501 370 and EP-407 870, the content of which is incorporated in the present description.
The polymerization processes which make use of the supported catalysts of the present invention can be carried out in liquid phase, in the presence or not of an inert hydrocarbon solvent. The solvent can be aliphatic such as, for example, propane, hexane, heptane, isobutene, cyclohexane, or aromatic such as, for example, toluene.
The polymerization processes which make use of the supported catalysts of the present invention can be advantageously carried out in gas phase.
The polymerization temperature is generally comprised between 0xc2x0 C. and 250xc2x0 C. In particular, in the processes for the preparation of HDPE and LLDPE, the polymerization temperature is generally comprised between 20xc2x0 C. and 150xc2x0 C. and, particularly, between 40xc2x0 C. and 90xc2x0 C. In the processes for the preparation of elastomeric copolymers the polymerization temperature is generally comprised between 20xc2x0 C. and 100xc2x0 C. and, particularly, between 30xc2x0 C. and 80xc2x0 C.
The molecular weight of the copolymers can be varied merely by varying the polymerization temperature, the type or the concentration of the catalytic components or by using molecular weight regulators such as, for example, hydrogen.
The molecular weight distribution can be varied either using mixtures of different metallocenes, or carrying out the polymerization in more steps which differ in the polymerization temperature and/or in the concentrations of the molecular weight regulator.
Polymerization yields depend on the purity of the metallocene component of the catalyst. Therefore, the metallocene compounds can be used in the supported catalysts of the invention either as such, or they can be subjected to purification treatments.
The polymers obtainable with the supported catalysts of the present invention are endowed with good morphological characteristics and can be obtained in form of spherical particles having diameters which can be comprised between 100 and 3000 xcexcm, depending on the catalyst and on the polymerization conditions used.
The following examples are given to illustrate and not to limit the invention.
The presence of functional groups on the supports was confirmed by I.R. analysis. The quantitative determination of the functional groups containing active hydrogen atoms was carried out by gas-volumetric measurement during the reaction of the supports with aluminium triethyl.
The porosities and surface areas were determined by nitrogen adsorption according to the method B.E.T. using an instrument SORPTOMATIC 1900 by Carlo Erba, as well as by mercury porosimetry by means of a POROSIMETER 2000 by Carlo Erba.
The intrinsic viscosities (I.V.) were measured in tetrahydronaphthalene at 135xc2x0 C.
The Differential Scansion Calorimetry measurements were carried out on an instrument DSC-7, of Perkin Elmer Co. Ltd., according to the following method. About 10 mg of sample were heated at 180xc2x0 C. with a scanning speed equal to 10xc2x0 C./min. The sample was kept at 18xc2x0 C. for 5 minutes and thereafter cooled with a scanning speed equal to 10xc2x0 C. Thereafter, a second scanning was carried out according to the same modalities of the first one. The values reported are those obtained in the second scanning.
The contents of the comonomer units in the copolymers were determined by I.R. analysis.
The absolute densities of the polymers were determined by density gradient columns according to the ASTM method D-1505.
The tamped bulk density (T.B.D.) and the poured bulk density (P.B.D.) were determined according to the method DIN-53194.
The preparation described in J. Ewen, J. Am. Chem. Soc., 1987, 109,6544, Suppl. mat. was followed.
Into a 2 litre two-necked round-bottomed flask, 50 g of indene (437 mmol) were dissolved under inert atmosphere with 500 ml of tetrahydrofuran and were cooled to xe2x88x9278xc2x0 C. By slow dropping (1 hour) 175 ml of n-butyllithium (2.5 M in hexane, 437.5 mmol) were added. The mixture was allowed to heat up to room temperature and was kept under stirring for 4 hours. It was cooled to xe2x88x9278xc2x0 C. and 40.42 g of dibromoethane (215 mmol) dissolved in 100 ml of tetrahydrofuran were dropped (within 20 minutes). After the end of the addition, the temperature was raised to 50xc2x0 C., the whole was kept under stirring for 12 hours, then was cooled down to room temperature and 20 ml of water were added. The organic phase was dried and the residue was extracted with pentane. By evaporation under vacuum 28.65 g of product were obtained (yield=51.6%).
Into a 250 ml two-necked round-bottomed flask provided with cooler, 8 g (31 mmol) of 1,2-bisindenylethane and 100 ml of anhydrous tetrahydrofuran were introduced, thus obtaining a yellow solution. After cooling to xe2x88x9278xc2x0 C., 40 ml of butyllithium (1.6 M in hexane, 64 mmol) were added dropwise, thus obtaining a precipitate which by heating dissolved again thus giving a reddish-yellow solution. Into a 250 ml four-necked round-bottomed flask, provided with cooler, 8.67 g of ZrCl4 (37.2 mmol) were introduced; this was cooled to xe2x88x92196xc2x0 C., and in this 50 ml of tetrahydrofuran were condensed (strongly exothermic reaction), the mixture was allowed to heat up to room temperature and thereafter it was heated under reflux for 40 minutes. At room temperature and while stirring, the solution of the lithium salt of bisindenylethane was added to the solution of the adduct ZrCl4/THF and was kept stirred for 20 hours in the dark. At 0xc2x0 C. gaseous HCl was bubbled in, thus obtaining a yellow solution together with a precipitate of the same colour. The solution was concentrated by evaporating under vacuum part of the solvent, was cooled to xe2x88x9220xc2x0 C. and filtered off. The precipitate was further purified by extraction with dichloromethane, thus obtaining 2.3 g (14.7%) of product.
The synthesis was carried out according to the method described in xe2x80x9cOrganometallics, 1990, 9, 3098xe2x80x9d (yield 54% from p-xylene).
38.2 g (265 mmol) of 4,7-dimethylindene were dissolved in 350 ml of tetrahydrofuran and the temperature of the solution was raised to 0xc2x0 C. Thereafter, 165 ml of n-butyl-lithium (1.6 M in hexane, 264 mmol) were added dropwise over 2.5 hours. After having allowed the whole to again reach room temperature and whilst stirring for 4 hours, a purple-red solution of 4,7-dimethylindenyllithium was obtained. This solution was cooled to xe2x88x9270xc2x0 C. and treated, dropwise for 35 minutes, with 25.3 g of 1,2-dibromethane (135 mmol) in 15 ml of tetrahydrofuran. After the temperature was raised again to room temperature, a light yellow solution was obtained to which water was added. The organic phase was collected and dried on Na2SO4. The solvent was then evaporated under vacuum and 20 g of product (yield 48%) were obtained.
A suspension of 10 g of 1,2-bis(4,7-dimethyl-3-indenyl)ethane (31.8 mmol) in 80 ml of tetrahydrofuran was added through a small tube to a solution of 2.82 g of KH (70.3 mmol) in 160 ml of tetrahydrofuran, kept under stirring. After the formation of hydrogen ceased, the resulting brown solution was separated from the excess KH. This solution and a solution of 12 g of ZrCl4 (THF)2 (31.8 mmol) in 250 ml of tetrahydrofuran were added, dropwise, over 3 hours, by means of a small tube, into a round bottomed flask containing 50 ml of tetrahydrofuran kept under rapid stirring.
A yellow solution and a precipitate were formed. After removal of the solvent under vacuum, the orange-yellow residue (mixture of racemo and meso isomers in the ratio 2.33:1 at the 1H-NMR analysis) was subjected to extraction with CH2C2 until all the orange product was completely dissolved. The yellow solid (1.7 g) resulted in being a single stereoisomer, that is the meso (yield 11.3%). After evaporation of CH2Cl2 from the orange solution, 4.9 g of an orange solid corresponding to a mixture of 93.7% racemo and 6.3% meso isomers (Yield 32.5%) was obtained. This solid was then recrystallized from toluene at xe2x88x9220xc2x0 C.
It was prepared according to the method described in xe2x80x9cH. H. Brintzinger et al., J. Organomet. Chem., 288, p.63 (1985)xe2x80x9d.
A commercial product (Schering, MW 1400) was used in a 30% b.w. toluene solution. After having removed the volatile fractions under vacuum, the vitreous material was ground up to obtain a white powder which was further treated under vacuum (0.1 mmHg) for 4 hours at a temperature of 40xc2x0 C. The powder thus obtained showed good flowability properties.